docs: エラッタを追加

[budougumi0617]

• ref: p50 GitHubの誤植 #89
• ref: p51 Minimal Version Selectionの実例について #90

[github-actions]

Code Metrics Report

	main (b08e287)	#91 (2e8c753)	+/-
Coverage	45.8%	45.8%	0.0%
Code to Test Ratio	1:0.9	1:0.9	0.0
Test Execution Time	11s	10s	-1s

Details

  |                     | main (b08e287) | #91 (2e8c753) | +/-  |
  |---------------------|----------------|---------------|------|
  | Coverage            |          45.8% |         45.8% | 0.0% |
  |   Files             |             26 |            26 |    0 |
  |   Lines             |            358 |           358 |    0 |
  |   Covered           |            164 |           164 |    0 |
  | Code to Test Ratio  |          1:0.9 |         1:0.9 |  0.0 |
  |   Code              |           4338 |          4338 |    0 |
  |   Test              |           3791 |          3791 |    0 |
+ | Test Execution Time |            11s |           10s |  -1s |

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Reported by octocov